Multi-die stacking using bumps with different sizes

ABSTRACT

A device includes a first die having a first side and a second side opposite to first side, the first side includes a first region and a second region, and a first metal bump of a first horizontal size formed on the first region of the first side of the first die. A second die is bonded to the first side of the first die through the first metal bump. A dielectric layer is formed over the first side of the first die and includes a first portion directly over the second die, a second portion encircling the second die, and an opening exposing the second region of the first side of the first die. A second metal bump of a second horizontal size is formed on the second region of the first side of the first die and extending into the opening of the dielectric layer. The second horizontal size is greater than the first horizontal size. An electrical component is bonded to the first side of the first die through the second metal bump.

TECHNICAL FIELD

This disclosure relates generally to integrated circuits, and moreparticularly to three-dimensional integrated circuits (3DIC) comprisinginterposers and the method of forming the same.

BACKGROUND

The integrated circuits have experienced continuous rapid growth due toconstant improvements in the integration density of various electroniccomponents (i.e., transistors, diodes, resistors, capacitors, etc.). Forthe most part, this improvement in integration density has come fromrepeated reductions in minimum feature size, allowing more components tobe integrated into a given chip area.

The volume occupied by the integrated components is essentially on thesurface of the semiconductor wafer. Although dramatic improvements inlithography have resulted in considerable improvements in 2D integratedcircuit formation, there are physical limitations to the density thatcan be achieved in two dimensions. One of these limitations is theminimum size needed to make these components. Also, when more devicesare put into one chip, more complex designs are required. An additionallimitation comes from the significant increase in the number and lengthof interconnections between devices as the number of devices increases.When the number and length of interconnections increase, both circuit RCdelay and power consumption increase.

Three-dimensional integrated circuits (3DIC) were thus formed, whereindies may be stacked, with wire-bonding, flip-chip bonding, and/orthrough-silicon vias (TSV) being used to stack the dies together and toconnect the dies to package substrates. In conventional die-stackingmethods, situation may arise that when two dies are bonded to anotherdie, the two dies may require different bump sizes, which causes thedifficulty in subsequent bonding, solder bump reflowing, underfillfilling, and wafer sawing steps.

SUMMARY

In accordance with one aspect, a device includes a first die having afirst side and a second side opposite to first side, the first sideincludes a first region and a second region, and a first metal bump of afirst horizontal size formed on the first region of the first side ofthe first die. A second die is bonded to the first side of the first diethrough the first metal bump. A dielectric layer is formed over thefirst side of the first die and includes a first portion directly overthe second die, a second portion encircling the second die, and anopening exposing the second region of the first side of the first die. Asecond metal bump of a second horizontal size is formed on the secondregion of the first side of the first die and extending into the openingof the dielectric layer. The second horizontal size is greater than thefirst horizontal size. An electrical component is bonded to the firstside of the first die through the second metal bump.

Other embodiments are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIGS. 1 through 8 are cross-sectional views of intermediate stages inthe formation of a three-dimensional integrated circuit (3DIC) includingstacked dies, wherein metal bumps having different sizes are formed on asame die/wafer.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative, and do not limit the scope of the disclosure.

A novel three-dimensional integrated circuit (3DIC) and the method offorming the same are provided. The intermediate stages of manufacturingan embodiment are illustrated. The variations of the embodiment arediscussed. Throughout the various views and illustrative embodiments,like reference numbers are used to designate like elements.

Referring to FIG. 1, wafer 100, which includes substrate 10 therein, isprovided. Substrate 10 may be formed of a semiconductor material, suchas silicon, silicon germanium, silicon carbide, gallium arsenide, orother commonly used semiconductor materials. In an embodiment, wafer 100is a device wafer comprising integrated circuits 12, which may includecomplementary metal-oxide-semiconductor (CMOS) transistors, resistors,inductors, capacitors, and/or the like. In alternative embodiments,wafer 100 is an interposer wafer that is substantially free from activedevices such as transistors. Furthermore, interposer wafer 100 mayinclude, or may be free from, passive devices such as capacitors,resistors, inductors, and/or the like. Accordingly, substrate 10 may beformed of a dielectric material such as silicon oxide.

Through-substrate vias (TSV) 16 are formed in substrate 10, and may beelectrically insulated from substrate 10 by insulation layers (notshown). TSVs 16 penetrate from one side of substrate 10 to the oppositeside. In an embodiment, wafer 100 is a device wafer, and the substrate10 has a first side 10 a and a second side 10 b opposite to the firstside 10 a. In integration process, the second side 10 b is referred toas the frontside of the substrate, and the first side 10 a is referredto as the backside of the substrate 10. Interconnect structure 18, whichincludes metal lines and vias (not shown) formed therein, is formed onthe second side 10 b of substrate 10 and electrically coupled tointegrated circuits 12. The metal lines and vias may be formed of copperor copper alloys, and may be formed using the well-known damasceneprocesses. Interconnect structure 18 may include a commonly knowninter-layer dielectric (ILD) and inter-metal dielectrics (IMDs), whichmay be low-k dielectric layers having low k values, for example, lowerthan about 2.5, or even lower than about 2.0. In alternativeembodiments, the side of wafer 100 facing up is the front side of devicewafer 100, while the side facing down is the bottom side. Metal bumps20, which may be solder bumps, are formed at a surface of wafer 100, andmay be electrically coupled to integrated circuits 12.

Interconnect structure 22 is formed on the first side 10 a of substrate10. Interconnect structure 22 includes one or more dielectric layer(s)24, and metal lines 26 and vias 28 in dielectric layer(s) 24. Metallines 26 and vias 28 are referred to as redistribution lines (RDLs)hereinafter. Dielectric layers 24 may be formed of polyimide, siliconnitride, organic dielectric materials, low-k dielectric materials, orthe like. RDLs 26/28 may be formed of copper or copper alloys, althoughother commonly used metals such as aluminum, tungsten, or the like, mayalso be used.

Under-bump-metallurgies (UBMs) 30 (including 30A and 30B) are formed andelectrically coupled to RDLs 26/28. UBMs 30 may be formed of aluminumcopper alloy, aluminum, copper, or the like, and each of UBMs 30 mayalso include a nickel layer over a copper-containing layer. Dielectriclayer 32 is formed to cover edge portions of UBMs 30, with the centralportions of UBMs 30 exposed through UBM openings 34A and UBM openings34B. UBM openings 34A are referred to as large UBM openings, while UBMopenings 34B are referred to as small UBM openings, although they areformed simultaneously. In an exemplary embodiment, the horizontal size(which may be a length or a width) L1 of UBM openings 34A is greaterthan the horizontal size L2 of UBM openings 34B, with ratio L1/L2 beinggreater than about 5, or even greater than about 10, for example.Carrier 35, which may be a glass wafer, may be bonded to a side of wafer100.

Next, as shown in FIG. 2, small metal bumps 36 are formed, wherein aportion of each of small metal bumps 36 is in one of small UBM openings34B. Small metal bumps 36 are electrically coupled to RDLs 26/28, andmay be electrically coupled to TSVs 16. In an embodiment, small metalbumps 36 are solder bumps such as eutectic solder bumps. In alternativeembodiments, small metal bumps 36 are copper bumps or other metal bumpsformed of gold, silver, nickel, tungsten, aluminum, and/or alloysthereof. When formed of copper, each of small metal bumps 36 may also becovered by a nickel layer, and/or a solder cap on the nickel layer (notshown).

In FIG. 3, die 38 is bonded to small metal bumps 36. Die 38 may be adevice die comprising integrated circuit devices, such as transistors,capacitors, inductors, resistors (not shown), and the like, therein, andmay be a logic die or a memory die. Depending on the structure of smallmetal bumps 36, the bonding between die 38 and metal bumps 36 may be asolder bonding or a direct metal-to-metal (such as a copper-to-copper)bonding. After die 38 is bonded to small metal bumps 36, underfill 40 isdispensed into the gap between die 38 and wafer 100, and is then cured.

Referring to FIG. 4, dielectric layer 44 is coated on wafer 100 and die38. Dielectric layer 44 may be a solder resist coating, which may beformed of a photo resist, a polymer, or polymer-like material.Alternatively, dielectric layer 44 may be formed of silicone, spin-onglass (SOG), solder resist, or the like. Dielectric layer 44 may includea portion directly over die 38, and a portion encircling die 38, smallmetal bumps 36, and underfill 40. Accordingly, dielectric layer 44protects small metal bumps 36 and the bonding between die 38 and wafer100. Dielectric layer 44 may be formed using spin coating, spraycoating, or ink jet print, followed by a curing step. Openings 46 arethen formed in dielectric layer 44, for example, using etching, so thatUBMs 30A are exposed.

Next, as shown in FIG. 5, large metal bumps 48 are formed in openings46, and may contact dielectric layer 44. In an embodiment, large metalbumps 48 are solder bumps, which may be formed of an eutectic solder, alead-free solder, or the like. In alternative embodiments, large metalbumps 48 are copper bumps, and may have nickel layers and/or solder capsthereon.

Next, as shown in FIG. 6, electrical component 50 is bonded to largemetal bumps 48. In an embodiment, electrical component 50 is a devicedie including integrated circuits such as transistors therein. Inalternative embodiments, electrical component 50 is a package substrate.In the embodiments large metal bumps 48 are solder bumps, a re-flow maybe performed to join electrical component 50 to large metal bumps 48.After the bonding, the bottom surface of electrical component 50 may behigher than the top surface of dielectric layer 44. Underfill 52 is thenfilled into the gap between electrical component 50 and wafer 100, andbetween large metal bumps 48. It is realized that although only one die38 and one die (electrical component) 50 is illustrated, there may be aplurality of dies 38 and dies 50 bonded to wafer 100. A die saw may beperformed at this time to separate wafer 100 into a plurality of dies,each including die 100′ (please refer to FIG. 7), which is a part ofwafer 100, one of dies 38, and one of dies 50.

After the bonding of electrical component 50 to wafer 100, thehorizontal size (which may be a length or a width) L3 of large metalbumps 48 is greater than the horizontal size L4 of small metal bumps 36,with ratio L3/L4 being greater than about 5, or even greater than about15, for example. Further, height H of large metal bumps 48 is greaterthan thickness T of dielectric layer 44.

Referring to FIG. 7, carrier 35 is de-bonded, and electrical component56, which may be a device die or a package substrate, is bonded to wafer100, wherein electrical component 56 and die 38 are on opposite sides ofwafer 100 (or die 100′). Optionally, as shown in FIG. 8, when electricalcomponent 56 is a device die, molding compound 58 may be formed to coverelectrical component 56. A die saw may then be performed to separatewafer 100 into a plurality of dies if the die saw has not been performedyet.

In the embodiments, large metal bumps and small metal bumps are formedin a same 3DIC. Since the small metal bumps are protected by adielectric material, the large metal bumps may be formed, and anotherdie may be bonded to the large metal bumps after the formation and thebonding of the small metal bumps, and no damage occurs to the smallmetal bumps during the bonding of the large metal bumps. This providesthe flexibility in the stacking of dies.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A device comprising: a first die having a firstside and a second side opposite to first side, the first side having afirst region and a second region; a first metal bump of a firsthorizontal size formed on the first region of the first side of thefirst die; a second die bonded to the first side of the first diethrough the first metal bump; a dielectric layer over the first side ofthe first die and comprising a first portion directly over the seconddie, a second portion encircling the second die, and an opening exposingthe second region of the first side of the first die; a second metalbump of a second horizontal size formed on the second region of thefirst side of the first die and extending into the opening of thedielectric layer, the second horizontal size being greater than thefirst horizontal size, wherein a top end of the second metal bump ishigher than a top surface of the dielectric layer; and a firstelectrical component bonded to the first side of the first die throughthe second metal bump.
 2. The device of claim 1, wherein the dielectriclayer comprises at least one of solder resist, photoresist, polymer, andsilicone.
 3. The device of claim 1, wherein the second metal bump has aheight greater than a height of the first metal bump.
 4. The device ofclaim 1, wherein a ratio of the second horizontal size to the firsthorizontal size is greater than about
 5. 5. The device of claim 1further comprising an underfill formed in a space between the firstelectrical component and the dielectric layer.
 6. The device of claim 1,wherein the first electrical component is a device die or a packagesubstrate.
 7. The device of claim 1, wherein the first die comprises afirst through-substrate via (TSV) formed inside the first die andelectrically coupled to the first metal bump, and a second TSV formedinside the first die and electrically coupled to the second metal bump.8. The device of claim 7 further comprising a second electricalcomponent bonded to the second side of the first die, and electricallycoupled to the first electrical component through the second TSV.
 9. Adevice comprising: a first die comprising a substrate having a firstside and a second side opposite to the first side; a firstthrough-substrate via (TSV) and a second TSV formed inside thesubstrate; a first under-bump-metallurgy (UBM) and a second UBM formedover the first side of the substrate and electrically coupled to thefirst TSV and the second TSV, respectively; a dielectric layer overlyingthe first UBM and the second UBM and having a first opening exposing atleast a portion of the first UBM and a second opening exposing at leasta portion of the second UBM, wherein the first opening has a firsthorizontal size smaller than a second horizontal size of the secondopening; a first metal bump of a first height formed on the exposedportion of the first UBM and extending into the first opening of thedielectric layer; a second metal bump of a second height formed on theexposed portion of the second UBM and extending into the second openingof the dielectric layer, wherein the first height is smaller than thesecond height; a second die bonded to the first die through the firstmetal bump; and a third die bonded to the first die through the secondmetal bump.
 10. The device of claim 9 further comprising a coating layerencircling the second die and the second metal bump, wherein a top endof the second metal bump is higher than a top surface of the coatinglayer.
 11. The device of claim 10, wherein the coating layer is a solderresist coating.
 12. The device of claim 9 further comprising anelectrical component bonded to the second side of the first die, andelectrically coupled to the third die through the second TSV.
 13. Thedevice of claim 9, wherein the second metal bump is a solder bump. 14.The device of claim 9, wherein a ratio of the second horizontal size ofthe second opening to the first horizontal size of the first opening isgreater than about
 5. 15. A device comprising: a first die having afirst side and a second side opposite to first side; a firstthrough-substrate via (TSV) and a second TSV formed inside the firstdie; a first under-bump-metallurgy (UBM) and a second UBM formed overthe first side of the first die and electrically coupled to the firstTSV and the second TSV, respectively; a dielectric layer overlying thefirst UBM and the second UBM and having a first opening exposing atleast a portion of the first UBM and a second opening exposing at leasta portion of the second UBM; a first metal bump of a first height formedon the exposed portion of the first UBM and extending into the firstopening of the dielectric layer; a second metal bump of a second heightformed on the exposed portion of the second UBM and extending into thesecond opening of the dielectric layer, wherein the first height issmaller than the second height; a second die bonded to the first diethrough the first metal bump; a third die bonded to the first diethrough the second metal bump; and a coating layer encircling the seconddie, the third die disposed over a top surface of the coating layer. 16.The device of claim 15 wherein a top end of the second metal bump ishigher than a top surface of the dielectric layer.
 17. The device ofclaim 15, wherein the coating layer is a solder resist coating.
 18. Thedevice of claim 15, wherein the first metal bump has a first horizontalsize and the second metal bump has a second horizontal size greater thanthe first horizontal size.
 19. The device of claim 15, furthercomprising an electrical component bonded to the second side of thefirst die, and electrically coupled to the third die through the secondTSV.
 20. The device of claim 15 wherein a top end of the second metalbump is higher than a top surface of the coating layer.